Antony Cotton, who plays Sean Tully, is thought to have been the subject of homophobic remarks, but it is unknown if he heard the comments as he made no complaint.

The memo says: "We have just been made aware of ­several recent instances of homophobic remarks being made on the studio floor.

"We are sure the vast majority of people working on Coronation Street find such behaviour unacceptable.

"But we'd like to make it absolutely clear that this is completely unacceptable. ITV has a bullying and harassment policy which clearly states that such behaviour may lead to disciplinary proceedings."

A source said: "This is an extremely worrying development. Coronation Street prides itself on being a tolerant and accepting place.

"One of our most popular actors, Antony Cotton, is gay and so is our outgoing executive producer Phil Collinson. We have had a number of gay characters on the Cobbles.

"The fact people are making homophobic jokes on set is unacceptable. And what makes this even more worrying is it seems this was not an isolated incident.

"It seems certain people were starting to make some really crude comments and that a nasty culture was developing. Cast and crew alike have been left in no doubt that anyone who continues to use homophobic language will be severely disciplined."